At least 20 House Republicans have now signed onto a petition to force a freewheeling immigration debate in the House, moving moderate Republicans toward the brink of driving a divisive issue to the House floor — one GOP leaders prefer to avoid ahead of the midterm elections.

Reps. John Katko, R-N.Y., and Dave Trott, R-Mich., signed on to the measure, known as a discharge petition, Wednesday. Trott is one of several retiring Republicans who have endorsed the petition, in addition to moderates facing tough reelection bids and others in districts with large Hispanic populations.

House Speaker Paul Ryan spoke out against the move again this week, calling it a “big mistake” after meeting privately with House Republicans on Wednesday.

“Like I said last week, obviously, we do not agree with discharge petitions,” Ryan, R-Wis., told reporters afterward. “We think they're a big mistake. They disunify our majority.”

Organizers of the petition need 218 signatures - five more Republicans, if all 193 Democrats back the measure - to kick off a debate and votes on four competing immigration proposals that deal with DACA recipients and border security.

If the effort secures 218 signatures, the motion to discharge is placed on a calendar and ripens for consideration on the second or fourth Monday of the month after a seven legislative day layover.

The discharge motion is debatable for only 20 minutes, split equally between proponents and opponents of the measure. If the motion to discharge a bill is adopted, the House would immediately consider the bill itself.

In this case, legislators are hoping to advance H.Res 744, bipartisan legislation introduced in March. The bill would allow the full House to debate as amendments a range of proposals for DACA, including Judiciary Committee Chairman Bob Goodlatte’s “Securing America’s Future Act.”

House Republican leaders have worked for months to advance the Goodlatte bill, but concede they are far short of 218 Republican votes needed to send it to the Senate.

With the threat of the discharge petition, GOP leaders are scrambling to fine-tune the Goodlatte bill in a desperate effort to build a Republican majority.

Ryan acknowledged that members of the GOP majority “fall into different camps” on immigration – but he said they want a solution on DACA and border security.

“That's why we met with the president, to advance a strategy that addresses the issues that our members have, the concerns they have, but doing it in a way where we actually have a process that can get a presidential signature, and not a presidential veto,” Ryan said. “And we're working with our members on that.”

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Two more bills that would advance to the floor during the debate are the bipartisan “Dream Act of 2017, introduced by Reps. Lucille Roybal-Allard, D-Calif., and Rep. Ileana Ros-Lehtinen, R-Fla.,” as well as the “USA Act of 2018,” fronted by Reps. Will Hurd, R-Texas, and Pete Aguilar, D-Calif.

Ryan would also be able to choose any other single piece of legislation to plug the fourth slot in the Queen of the Hill approach.

Under Queen of the Hill rules, if more than one alternative obtains a majority, the winner is the one that receives the greatest number of votes. It is unclear if any of the competing measures would garner a majority.

For months, Ryan has warned his colleagues against advancing a measure he thinks President Trump would veto.

“We want to advance something that has a chance of going into law, where the president would support it,” Ryan said.

Minority Leader Nancy Pelosi, meanwhile, is cheering for the discharge petition to succeed.

“We believe that this bipartisan bill that the members have put together, who share the value of protecting the DREAMers, is the bill that would win if they would just give us a vote, give us a chance.”

House Republicans used a discharge petition successfully in 2015 to force a vote to reauthorize the Export-Import Bank.

As they battle a revolt on their left flank, GOP leaders are also struggling with House conservatives over the farm bill. Some hard-right members are demanding a floor vote on a conservative immigration bill from Rep. Bob Goodlatte, R-Virginia, in exchange for their support of the farm bill, which is expected to pass on Friday, approving billions in farm subsidies and nutrition programs including food stamps.

There is no time limit to gather 218 signatures on the discharge petition, but an incomplete effort expires at the end of the 115th Congress next January.